Pneumatic transmission systems are widely used to transmit articles and written information from one place to a remote location. The devices comprise both single and twin tube types in which the carrier is impacted against an end object at the end of the travel. This is undesirable in that the impact subjects the carrier and the terminal to needless wear and tear. In single tube systems it is undesirable to intake or discharge air from the end terminal.
Attempts to control the impact has generally been in the area of sensor switches which open and close various valves to control the air pressure or to deliver into a box with a door on it with carrier deceleration against a dead column of air. These are expensive to install and maintenance is required often because of the location and nature of the carrier moving through the transmission tube at a speed of approximately 25 feet per second. Other types of systems have utilized a closed carrier terminal at both ends in which a door must be opened in order to allow removal of the carrier from the terminal box. This is undesirable in that it requires more moving parts and more technical expertise in operating the device. It is undesirable to discharge or intake air into a transmission line because the warm air moving into the line causes condensation to develop. In addition, open lines to discharge the air create noise. Air is ejected into the building and heating or air conditioning problems occur.